Recent years, an illumination device using a light emitting diode (LED) having long life and small power consumption that is said to be environmentally friendly has become commercially practical along with improvement of light emission efficiency and increase of light emission intensity. In addition, since development of a blue color LED chip, there are developed a white color LED light source which emits white color light by combination of the blue color LED chip and a fluorescent material which emits excitation light having a predetermined wavelength excited by the light from the LED chip, and a white color LED light source which synthesizes white color light using three primary color LED chips including the blue color LED chip, a green color LED chip, and a red color LED chip.
Therefore, as a backlight of a liquid crystal display device or the like, there is used an illumination device (LED backlight device) in which the white color LED light sources are arranged. In addition, as a backlight of a liquid crystal display device or the like, there are known a direct type backlight device in which the light sources are disposed behind the display screen and an edge-light type backlight device in which the light sources are disposed on lateral sides of the display screen, a light guide plate is disposed behind the display screen, light enters the light guide plate from the lateral sides of the display screen, and the light is reflected inside the light guide plate so as to be emitted from a light emission surface of the light guide plate in a planar manner.
Because the edge-light type backlight device has a structure in which a light source portion is disposed on the lateral side of the display screen while a plate-like light guide plate is disposed behind the display screen, it is easy to be thin and is preferable for realizing a thinner liquid crystal display device or the like. On the other hand, the direct type backlight device has a structure in which the light source is disposed behind the display screen and directly illuminates the same, and hence it is easy to realize high luminance illumination and is preferable because light emission luminance can be easily controlled for each area.
In addition, each LED light source is constituted of an LED package in which the LED chip is mounted on a sub mount substrate and is sealed by transparent resin or transparent resin containing a predetermined fluorescent material to form the package. A plurality of the LED packages are integrally arranged on an LED mounting substrate to form a module, which is a light emission module (LED module) having a predetermined shape.
In addition, in the direct type backlight device, in order to diffuse light emitted from the LED light sources to be uniform, optical members such as a diffusing plate and a lens sheet are disposed. An example of the liquid crystal display device including such the backlight device is described with reference to FIG. 12.
As illustrated in the diagram, a liquid crystal display device 69 includes a liquid crystal panel 59, an LED backlight device 49 which supplies light to the liquid crystal panel 59, and a housing HG (a front housing HG1 and a back housing HG2) which sandwich these members.
The liquid crystal panel 59 includes an active matrix substrate 51 including switching elements such as thin film transistors (TFTs) and an opposing substrate 52 which is opposed to the active matrix substrate 51, which are adhered to each other with a seal material (not shown). Then, liquid crystal (not shown) is injected into a gap between the substrates 51 and 52.
Note that polarizing films 53 are attached to the light receiving plane side of the active matrix substrate 51 and the light emitting side of the opposing substrate 52. Then, the above-mentioned liquid crystal display panel 59 displays an image by utilizing a change of transmittance due to tilt of liquid crystal molecules.
The LED backlight device 49 disposed immediately below the liquid crystal display panel 59 includes an LED module MJ, a backlight chassis 41, a reflection sheet 42, a diffusing plate 43, a prism sheet 44, and a lens sheet 45. The LED module MJ is constituted of a plurality of point-like light sources 1 mounted on a mounting plane 21U of an LED mounting substrate 21.
The LED mounting substrate 21 is a plate-like and rectangular substrate having the mounting plane 21U on which a plurality of electrodes (not shown) are arranged. Further, the point-like light sources 1 as packages of LED light sources, for example, are mounted on the electrodes. Each of the point-like light sources (LED light sources) 1 includes a sub mount substrate on which an LED chip is mounted. Then, the electrode and the LED chip are electrically connected to each other via the sub mount substrate.
Note that a resist film (not shown) to be a protective film is formed on the mounting plane 21U of the LED mounting substrate 21. The resist film has white color having reflecting properties, for example. It is because even if light enters the resist film, the light is reflected by the resist film and is directed to the outside, and hence a cause of light intensity unevenness due to light absorption by the mounting substrate 21 is canceled.
In addition, in the illustrated LED backlight device 49, for example, there are mounted relatively short mounting substrates 21, on each of which five point-like light sources 1 are mounted in a row, and relatively long mounting substrates 21, on each of which eight point-like light sources 1 are mounted in a row.
In this way, the row of five point-like light sources 1 and the row of eight point-like light sources 1 are arranged to make a row of thirteen point-like light sources 1, and further the two types of mounting substrates 21 are arranged also in a direction crossing (perpendicular to) the direction in which the thirteen point-like light sources 1 are arranged (Note that the point-like light sources 1 are arranged at equal spaces). In addition, the arrangement pattern and the number of the arranged point-like light sources are appropriately changed in accordance with a size of the screen, required luminance, and the like.
Thus, the point-like light sources 1 are arranged in a lattice (namely, the LED modules MJ are arranged in a planar manner), and light rays from the point-like light sources 1 are mixed to form planar light (Note that for convenience sake, the direction in which different types of mounting substrates 21 are arranged is referred to as an X direction, while the direction in which the same type of mounting substrates 21 are arranged is referred to as a Y direction, and the direction perpendicular to the X direction and the Y direction is referred to as a Z direction).
The backlight chassis 41 is a box-like member, for example, and houses a plurality of LED modules MJ which are spread over on a base 41B thereof. Note that the base 41B of the backlight chassis 41 and the LED mounting substrate 21 of the LED module MJ are connected by means of rivet (not shown) or the like. In addition, the reflection sheet 42, the diffusing plate 43, the prism sheet 44, and the lens sheet 45 are stacked in this order on the backlight chassis 41.
The reflection sheet 42 is an optical sheet having a reflection surface 42U and covers the plurality of LED modules MJ so that the backside of the reflection surface 42U faces the same. However, the reflection sheet 42 has through holes 42H at positions corresponding to the point-like light sources 1 so that the light emission surfaces of the point-like light sources 1 are exposed from the reflection surface 42U.
Then, when a part of light emitted from the point-like light source 1 propagates toward the base 41B of the backlight chassis 41, the light is reflected by the reflection surface 42U of the reflection sheet 42 so as to propagate to separate from the base 41B. Therefore, because the reflection sheet 42 exists, a loss of light from the point-like light sources 1 is suppressed, and the light is directed toward the diffusing plate 43 opposed to the reflection surface 42U.
The diffusing plate 43 is an optical sheet overlaying the reflection sheet 42 so as to diffuse light emitted from the LED module MJ and the reflection light from the reflection sheet 42U. In other words, the diffusing plate 43 diffuses the planar light formed by the plurality of LED modules MJ (namely, the plurality of point-like light sources 1 arranged in a matrix) so that the light reaches the entire region of the liquid crystal display panel 59.
The prism sheet 44 is an optical sheet overlaying the diffusing plate 43. Further, the prism sheet 44 includes triangular prisms, for example, each of which extends in one direction (linearly), and the triangular prisms are arranged in the direction perpendicular to the one direction in the sheet plane. Thus, the prism sheet 44 deflects the light radiated from the diffusing plate 43. Note that the prisms extend in the Y direction in which smaller number of the point-like light sources 1 are arranged and are arranged in the X direction in which larger number of the point-like light sources 1 are arranged.
The lens sheet 45 is an optical sheet overlaying the prism sheet 44. Further, fine particles for refracting and scattering light are dispersed inside the lens sheet 45. Thus, the lens sheet 45 prevents the light from the prism sheet 44 from concentrating locally so as to suppress a difference between bright and dark parts (light intensity unevenness).
Then, the above-mentioned LED backlight device 49 allows the planar light formed by the plurality of LED modules MJ to pass through the plurality of optical sheets 43 to 45 to be supplied to the liquid crystal panel 59. Thus, the non-light emission type liquid crystal panel 59 receives light (backlight light) from the LED backlight device 49 so as to improve its display function.
As described above, in the LED backlight device having the conventional structure, the LED light source is used as the point-like light source, and the plurality of LED light sources are arranged in a lattice, for example, so as to form a planar light emission body. Therefore, various techniques are used for suppressing luminance unevenness and color unevenness due to the LED light sources as the point-like light sources. There are already disclosed a backlight device equipped with a processing portion for adjusting intensity of light emitted immediately above the LED (see, for example, Patent Document 1) and a backlight device equipped with a lens having an optical function for scattering and diffusing light (see, for example, Patent Document 2).